Many micro-fluid ejection apparatuses are controlled by data signals, such as those which cause fluid, such as ink for example, to be applied to a medium such as paper. An ink jet printing apparatus, for instance, may include a micro-fluid ejection head, such as a printhead having actuators that are controlled by data signals. In particular, the printhead can reside on a micro-fluid ejection device, such as a printhead cartridge having an ink reservoir and an actuator chip. The chip can include nozzles with corresponding actuators, such as heaters. A main electronic controller within the printing apparatus can transmit voltage signals to the printhead. If standard CMOS voltage signals are utilized, typically a 3.3 V signal represents a digital 1 while 0V represents a digital 0. The voltage signals cause the heaters to heat the ink held in a chamber at the nozzles, which in turn causes the ink to be ejected from the nozzles onto the print medium at selected ink dot locations within an image area. In response to the signals, a carrier might move the printhead relative to the medium, while the ink dots are jetted onto selected pixel locations (although in other embodiments, a stationary printhead, such as a page-wide printhead, might be used).
Users of printing apparatuses, such as the above, continue to demand higher quality images and text which require higher resolution, or, in other words, that more dots be printed per unit area. Users also continue to demand higher print speeds, such that pages can be printed faster. In order to decrease the time required to print an image or increase the resolution of a printed image, larger and larger numbers of nozzles are being placed on modern ink jet printhead cartridges. Moreover, speed can be increased by increasing the power of the circuit driving the voltage signals being delivered from the main controller to the printhead.
However, increased number of nozzles and increased power can also increase the electromagnetic interference (EMI) generated by the ejection apparatus. Increased EMI can interfere with, for example, internal printing components and electronics, as well as external devices that may be located near the ejection apparatus. In fact, the Federal Communications Commission establishes standards on the limits of EMI that may be emitted from a device. Accordingly, in order to stay within the EMI standards, power levels are often limited, thereby limiting the speed at which data can be transmitted and therefore the speed at which the apparatus may print. While improved techniques have been developed for transmitting voltages in micro-fluid ejection apparatus, such as via lower voltage differential signaling, such techniques can still create high levels of EMI.
Thus, there is a need to increase the speed of data communication in a micro-fluid ejection apparatus, such as the communication between the printer electronics of a printing apparatus and a printhead cartridge, while controlling EMI within acceptable levels.